To map the fine-touch pressure thresholds
of the adult penis in circumcised and uncircumcised men, and
to compare the two populations.

SUBJECTS AND METHODS

Adult male volunteers with no history of
penile pathology or diabetes were evaluated with a
Semmes-Weinstein monofilament touch-test to map the
fine-touch pressure thresholds of the penis. Circumcised and
uncircumcised men were compared using mixed models for
repeated data, controlling for age, type of underwear worn,
time since last ejaculation, ethnicity, country of birth, and
level of education.

RESULTS

The glans of the uncircumcised men had
significantly lower mean ( SEM ) pressure thresholds than
that of the circumcised men, at 0.161 (0.078) g ( P =
0.040) when controlled for age, location of measurement, type
of underwear worn, and ethnicity. There were significant
differences in pressure thresholds by location on the penis (
P < 0.001). The most sensitive location on the
circumcised penis was the circumcision scar on the ventral
surface. Five locations on the uncircumcised penis that are
routinely removed at circumcision had lower pressure
thresholds than the ventral scar of the circumcised
penis.

CONCLUSIONS

The glans of the circumcised penis is
less sensitive to fine touch than the glans of the
uncircumcised penis. The transitional region from the
external to the internal prepuce is the most sensitive region
of the uncircumcised penis and more sensitive than the most
sensitive region of the circumcised penis. Circumcision
ablates the most sensitive parts of the penis.

KEYWORDS

circumcision, pressure sensitivity,
penis

CIRP Note: This paper, which was published on
Monday, March 19, 2007, is likely to be a landmark in the
understanding of penile innervation and penile sensitivity.
This file is incomplete at this time. Two graphic
illustrations, three tables, and one graph will be added in
the near future to complete the file. The abstract, text, and
references are complete.

INTRODUCTION

Infant male circumcision, the most common
medical procedure in the USA, might also be the most
divisive. The long-term health impact of neonatal
circumcision has received little study, while the
consequences of circumcision on sexual function in the adult
male have received even less attention.

A poorly documented study by Masters and
Johnson, briefly mentioned only in their book [1] and never subjected to peer-review, claimed
to find no difference in the finetouch perception of the
glans of circumcised and uncircumcised men. Several studies
assessed the impact of circumcision on sexual function in
adult men [2–6]. These studies had
few subjects, a relatively short follow-up and a reliance on
subjective self-reporting obtained from men with a history of
penile and sexual dysfunction. Notable in these studies is
the high percentage (27.3% [4] to 64.2% [6]) of subjects who were circumcised to
correct a penile problem, and who reported no improvement
after surgery, a decrease in penile sensitivity, or a
reduction in erectile function.

Bleustein et al. [7], in a comparison study of men with and with
no erectile dysfunction (ED), using quantitative
somatosensory testing that included vibration, pressure,
spatial perception, and warm and cold thermal thresholds,
found that uncircumcised men had worse vibratory sensation
and better fine-touch sensation. These differences
disappeared when controlled for age, hypertension and
diabetes.

Whether the penis is circumcised or not
might also affect coitus. For women, having a male partner
with a foreskin increased the duration and comfort of coitus
and increased the likelihood of achieving single and multiple
orgasms [8]. A recent multinational
population survey using stopwatch assessment of the
intravaginal ejaculation latency time (IELT) found that
Turkish men, the vast majority of whom are circumcised, had
the shortest IELT. When Turkish men were excluded from the
analysis, there was no difference between circumcised and
uncircumcised men [9]. Likewise, in a
London population, men from Islamic countries were more
likely to have premature ejaculation [10].

The type of nerve endings in the penis
vary with location. The glans penis primarily has free nerve
endings that can sense deep pressure and pain [11]. The transitional area from the external
to the internal surface of the prepuce, or ‘ridged
band’, has a pleated appearance that is continuous with
the frenulum and has a high density of fine-touch
neuroreceptors, such as Meissner’s corpuscles [12–14]. Based on this histology, the
transitional region and the ventral surface of the prepuce
would be expected to have lower thresholds for light
touch.

Controversy over the sensory consequences
of infant male circumcision on adult sexual function has been
fuelled by a lack of objective data. By objectively measuring
penile sensitivity, the present study aimed to map the
fine-touch pressure thresholds of the penis and quantify the
differences in penile sensitivity between men with and
without foreskins.

SUBJECTS AND METHODS

Subjects were recruited by posting ‘fliers’ at
the San Francisco Bay Area medical school. Also,
announcements were made on a medical radio programme, and
advertisements were placed in local Bay Area general
circulation newspapers.

Subjects were men aged > 18 years in
good health, with no genital alterations, except for
circumcision, as determined by healthscreening questions. A
short questionnaire was completed to determine ethnicity,
place of birth, highest education degree obtained, type of
underwear worn, timing of last ejaculation, referral source,
and health status. Circumcision status was determined by a
physical examination.

Exclusion criteria were: transsexuals;
intersex individuals; males born with abnormal genitals, e.g.
hypospadias; a history of diseases or conditions known to
affect sexual sensitivity and function, e.g. diabetes
mellitus; a history of genital, prostate, or urinary tract
disease of any kind, including but not limited to sexually
transmitted diseases, open sores, or lesions at the time of
screening; prostatitis; prostate cancer; BPH; spinal cord
injury; peripheral nerve injury; peripheral neuropathy;
sciatica; any penile piercing; penile enlargement surgery;
any form of psychiatric condition; or a history of alcohol or
substance abuse. Informed consent was obtained before
testing.

The fine-touch sensitivity of 19
locations on the penis was measured using Semmes- Weinstein
monofilament touch-test sensory evaluators (North Coast
Medical Supply, Morgan Hill, CA, USA) [15–17] to create a penile sensitivity
map (Figs 1 and 2) On the dorsum of the penis, these
locations were: (1) the shaft proximal to coronal ridge; (2)
the outer prepuce; (3) the rim of the preputial orifice; (4)
the muco-cutaneous junction; (5) the ridged band; (6) the
preputial mucosa; (7) the coronal sulcus; (8) the coronal
ridge; (9) the middle of dorsal aspect of the glans; (10) the
glans at the meatus; on the ventral surface of the penis, the
locations were (11) the coronal ridge; (12) the frenulum at
the urethral slit; (13) the frenulum near the ridged band;
(14) the frenulum at the mucocutaneous junction; (15) the rim
of the preputial orifice; (16) the outer prepuce; (17) the
shaft proximal to the coronal ridge; and locations pertaining
to circumcised men only (18) the circumcision scar on the
dorsal surface and (19) the circumcision scar on the ventral
surface. Locations 2–5 and 13–16 were measured
only in uncircumcised men because these locations are ablated
by circumcision.

Because of the method of data collection,
it was impossible for the physician measuring the fine-touch
thresholds to be unaware of the circumcision status of the
subject. Likewise, because of the number of locations
sampled, it was also impossible for the statistician to be
unaware of the circumcision status of the subject.

Based on unpublished pilot data, it was
determined that sampling 50 uncircumcised and 150 circumcised
men would have 80% power to show a difference of 0.046 g with
a type I error of 5%. Demographic information by circumcision
status were compared using Mantel-Haenszel, Fisher’s
exact, chi-square and t -tests. Fine-touch pressure
thresholds by location were compared using t -tests
and linear regression. Mixed models for repeated data on
single subjects stratified by location of measurement, which
control for withinsubject variability, were developed using
locations present in both the circumcised and the complete
penis. Models were assessed using forward, backwards and
stepwise selection. Similar models were developed using only
locations on the glans penis. This study protocol was
approved by the Western Institutional Review Board.

RESULTS

In all, 163 subjects were enrolled; one
uncircumcised man was excluded for diabetes, two
uncircumcised men and one circumcised man were excluded for
hypospadias. All of the men completed the testing once it
started. A comparison of the demographic information by
circumcision status is shown in Table 1. Men born outside the
USA were eight times more likely to be uncircumcised.

Fine-touch pressure thresholds for each of the penile
positions is shown in Table 2 and Fig. 3. The region most
sensitive to fine touch on the circumcised penis was the
circumcision scar. The ventral scar was more sensitive than
the dorsal scar ( t -test and signtest P <
0.001). In all but one position, finetouch pressure
thresholds were greater in the circumcised penis. The most
sensitive regions in the uncircumcised penis are those
removed by circumcision. There was no interaction between age
and circumcision status.

When compared with the most sensitive
area of the circumcised penis, several locations on the
uncircumcised penis, which are missing from the circumcised
penis, were significantly more sensitive (Table 2).

There was no association between
fine-touch pressure threshold and the ambient room
temperature at the time of the examination, the time since
the reported last ejaculation ( P = 0.659), or the
country of birth.

Using a mixed model to evaluate repeated measures,
location of the measurement, age, wearing briefs, level of
education, being Hispanic, and circumcision status were all
statistically significant in the multivariate models (Table
3), e.g. with each year of age, the fine-touch pressure
threshold increased by 0.011 or 0.013 g.

DISCUSSION

The glans in the circumcised male is less
sensitive to fine-touch pressure than the glans of the
uncircumcised male. The most sensitive location on the
circumcised penis is the circumcision scar on the ventral
surface. Five locations on the uncircumcised penis that are
routinely removed at circumcision were more sensitive than
the most sensitive location on the circumcised penis.

Despite the controversy over the
long-term impact of male circumcision, no thorough,
objective, quantitative studies measuring the long-term
sensory consequences of infant circumcision have hitherto
been reported. The present study provides the first extensive
mapping of the fine-touch pressure thresholds of the adult
penis. This information provides a baseline for future
comparison studies and provides investigators with the
testing locations that provide the most differentiation.

The Semmes-Weinstein monofilaments are
individually calibrated to deliver a targeted force within a
5% SD. They have been used to test female genital sensitivity
[17] and can be used to determine changes
in sensitivity over time.

It is difficult to compare our data and
results with those claimed by Masters and Johnson [1]; no method is documented, only their
assertion of no difference in fine-touch reception on the
glans. Nevertheless, their results, even if they were
verifiable, are of little value to the question of the
long-term sensory consequences of infant circumcision. First,
the glans has virtually no fine-touch neuroreceptors [11–14]. Second, when determining the
aggregate sensory impact of circumcision, the sensory effects
of circumcision on the glans are of secondary significance,
because the glans is not removed during circumcision. Instead
of measuring changes in the glans after circumcision, it is
more important to measure the sensory investment of the parts
of the penis removed by circumcision.

In a subjective study with only a 44%
response rate, Fink et al. [2]
questioned men, using an unvalidated survey tool that they
hoped would measure sexual function. Compared to before
circumcision, men reported reduced erectile function (
P = 0.01), decreased penile sensitivity ( P =
0.08), no changes in sexual activity, and improved
satisfaction after circumcision. The circumcisions were for
‘medical reasons’ in 88%. For a procedure that
was expected to correct their problem, entirely favourable
outcomes would be expected, but 38% reported a perceived
problem or difficulty as a result of the procedure.

Collins et al. [3] studied 15 men who were circumcised as
adults; all but one had a penile problem. The patients
completed the Brief Male Sexual Function Inventory, an
unvalidated measure of sexual function, before and at least
12 weeks after the procedure. Not surprisingly, this
underpowered study failed to find any differences in sex
drive, erection, ejaculation, problem assessment, or overall
satisfaction. This is an intriguing finding because the men
were circumcised expecting an improvement in sexual function
and satisfaction.

In a study designed to measure the impact
of anterior urethroplasty on erectile function, Coursey et
al. [4] included a control group of men
who were circumcised for ‘phimosis or other benign
indication’. Of the 48 men circumcised, only 22 (46%)
completed the survey. Using an internally validated survey,
27% reported worsening satisfaction with their erectile
function after a procedure.

In a Turkish population of 42 men in
their third decade undergoing circumcision, 39 of whom sought
circumcision for religious reasons, the Brief Male Sexual
Function Inventory, measured before and at least 12 weeks
after the procedure, showed no difference in any of the five
areas assessed by the instrument. However, the mean IELT was
significantly longer after circumcision (P=0.02) [5]. As noted earlier, Turkish men had the
shortest mean IELT of the countries assessed [9].

In a study of 125 men drawn from a
urology clinic, Bleustein et al. [7]
found that uncircumcised men, both with and with no erectile
dysfunction, had lower thresholds for pressure using the same
device as used in the present study. The differences they
found were no longer statistically significant when adjusted
for age, diabetes, and hypertension. Their age difference (7
years) was greater than in the present population. Their
population consisted of patients referred to a urologist; the
present subjects were drawn from the general population, and
diabetics were excluded. We did not enquire about
hypertension nor measure blood pressure. Bleustein et
al. only sampled two locations, the meatus and the dorsal
glans halfway between the meatus and the corona, in
circumcised men, with an additional sample in uncircumcised
men at the ‘dorsal midline foreskin’ with the
prepuce in its natural position over the glans. In
uncircumcised men, there were no significant differences
between the measurements taken at the glans with the foreskin
retracted and those taken at the level of the glans with the
foreskin in its normal position. The positions used in that
study correlate to positions 9, 10 and 16 in the present
study. In our mixed model, controlling for location of the
measurement, age, wearing briefs, being Hispanic, and
circumcision status, position 10 had a lower threshold than
position 9 (0.243 g, SEM 0.079, P<0.002). The
present data indicated that the location on the uncircumcised
penis measured by Bleustein et al. had one of the
highest thresholds of the locations found only on the
uncircumcised penis. We found that the age-adjusted
thresholds were significantly lower in location 16 than
either 9 or 10 (location 9, - 0.75 g, SEM 0.184, P
< 0.001; location 10, - 0.56 g, 0.17, P <
0.002).

The studies detailed above share several
important flaws: (i) a low response rate to opportunities to
complete surveys (it is speculative as to how the half who
did not complete these surveys would have responded); (ii)
the lack of agreed upon, externally validated instruments to
measure erectile function; (iii) small population sizes that
limit the study power; (iv) the subjective nature of
instruments used; (v) short followup times; and (vi) the
patients in the studies were not genitally healthy.

The last three items deserve special
comment. Self-reporting is notoriously unreliable, and all
but one of the reported studies relied on patient testimony
rather than objective measurements. Patients are highly
susceptible to suggestions or inferences that surgery or
treatments used to correct a problem will, in fact, correct
that problem. Also, otherwise healthy men who seek
circumcision for other than medical reasons are predisposed
to reporting a favourable outcome. Furthermore, surveys with
subjective measures are dependent on the respondent’s
state of health. When asked to rate quality of life of
various impaired health states, healthy individuals will rate
the quality lower than will a person in that particular
health state. In these studies, it would be expected that the
men rate their genital performance higher when in the
genitally impaired condition than if they were not genitally
impaired.

The short follow-up might have precluded
changes in genital response and sensitivity that take longer
to develop. Likewise, the acute changes from surgery and scar
remodelling are known to take up to 12 months to resolve [18]. Finally, except for the Turkish study,
the men in these studies had penile pathology. Consequently,
improvements in this population would be expected regardless
of the intervention, due to what is commonly referred to as
the ‘floor effect’ (more room for improvement
than deterioration). Consequently, the worsening in so many
subjects is remarkable. It could be concluded that
circumcision might be an invalid intervention for these
medical conditions.

The present subjects, while drawn from
the general population, were men who showed the initiative to
participate. This might introduce a population and selection
bias, but the objective nature of the measure should not have
been affected. In the USA, uncircumcised men are
demographically different from circumcised men. They tend to
be younger and from certain ethnic backgrounds. They might
also be from families with either higher or lower parental
education levels, depending on the decade of their birth [19,20]. Younger men might have been less
willing to participate in the study due to their increased
modesty. As there are many more circumcised than
uncircumcised men in the USA, recruiting equal numbers of
subjects from each group was challenging. The measurement of
fine touch using pressure thresholds might be limited. Fine
touch transmitted through Meissner’s corpuscles might
be dynamic, using a network of nerve endings. For example,
the fingertips, which have a high density of Meissner’s
corpuscles, are able to interpret Braille when moving
over raised dots, not merely by pressing on
them. Consequently, a static measurement of pressure
threshold can miss much of what the Meissner’s
corpuscles are capable of transmitting. An instrument that
measures the sensitivity to light brushing or that can
discriminate surface texture when rubbing might be needed to
measure this dynamic sensation.

The differences in age, based on
circumcision status, were expected. In their study, Bleustein
et al. [7] found that uncircumcised
men were a mean of 7 years older. Based on the fluctuations
of circumcision rates over the past century, we expected
genital integrity to be more prominent among older men and
among men in their twenties. Because the confidence,
sufficient to volunteer for mapping of genitalia, might not
come until the later twenties, this population might have
been under-represented in our study.

Additional study with vibratory, hot and
cold thresholds on a wider variety of positions on the penis
is needed. Furthermore, development of a reliable method of
measuring dynamic sensation is needed to identify, elucidate
and quantify the sensory capacity of the various nerve
endings in all parts of the penis, and to provide a greater
understanding of the dynamic sensory interplay between the
various parts of the uncircumcised penis during sexual
activity. Finally, prospective real-time stopwatch
assessments of the IELT at coitus in men, investigated in the
laboratory by the Semmes- Weinstein touch test, would provide
additional objective information of their sexual and
particularly ejaculatory performance. Long-term monitoring of
numerous factors of sexual pattern, including sexual pattern
films, would provide additional information. Ideally, such
investigations could be undertaken on adult subjects before
and after elective circumcision, and in whom there is no
preoperative pathology.

In conclusion, circumcision removes the
most sensitive parts of the penis and decreases the
fine-touch pressure sensitivity of glans penis. The most
sensitive regions in the uncircumcised penis are those parts
ablated by circumcision. When compared to the most sensitive
area of the circumcised penis, several locations on the
uncircumcised penis (the rim of the preputial orifice, dorsal
and ventral, the frenulum near the ridged band, and the
frenulum at the muco-cutaneous junction) that are missing
from the circumcised penis were significantly more
sensitive.

ACKNOWLEDGEMENTS

Author contributions: Morris L. Sorrells,
MD, James L. Snyder, MD, Mark D. Reiss, MD, and Christopher
Eden, MD contributed to the conception and design of the
study, the acquisition of data, revision of the manuscript,
and approved the final version. Marilyn F. Milos, RN
contributed to the conception and design of the study, the
acquisition of data, the interpretation of the data, obtained
funding, revision of the manuscript, and approved the final
version. Norma Wilcox, RN contributed to the conception and
design of the study, revision of the manuscript, and approved
the final version. Robert S. Van Howe, MD, MS contributed to
the design of the study and the analysis and interpretation
of the data, drafted the article and revised it critically,
and approved the final version.

CONFLICT OF INTEREST

None declared. Source of funding:
National Organization of Circumcision Information Resource
Centers. The director of National Organization of
Circumcision Information Resources Centers (MFM) was involved
in the design and conduct of the study; collection and
interpretation of the data; and review, or approval of the
manuscript.